1. Field of the Invention
This invention relates to an audio system for a vehicle which is carried on a vehicle such as a passenger car to enjoy audio information such as music.
2. Description of the Prior Art
Audio systems for a vehicle normally include a plurality of front loudspeakers and a plurality of rear loudspeakers all of which have the same characteristics. In this instance, the sound field produced by the front and rear loudspeakers does not make a forwardly displaced sound field. The forwardly displaced sound field herein denotes a sound field in which the position at which sounds from the front and rear loudspeakers are heard equally loudly is displaced forwardly from a geographical central position among the front and rear loudspeakers to another position of or around a driver's seat of the vehicle.
However, in order to assure safe driving of a vehicle, an audio system for a vehicle is sometimes constructed such that a plurality of front loudspeakers produce sound in medium and high frequency sound regions and a plurality of rear loudspeakers produce sound in a low frequency sound region so as to make the sound field a forwardly displaced sound field.
Since the conventional audio systems for a vehicle are constructed in such a manner as described above, when the sound field is not a forwardly displaced sound field, various switches of an equalizer, a fader and so forth must be manually operated in accordance with the number and positions of passengers of the vehicle to adjust the sound field, which is a very cumbersome operation.
Further, if the sound volume is excessively great, then a passenger on the rear seat will feel sound in medium and high frequency sound regions disagreeable due to reflected sound from the rear windshield and so forth of the vehicle.
Meanwhile, when the sound field is a forwardly displaced sound field, if the sound volume is small, then a more effort will be required for a passenger on the rear sheet to listen to sound in medium and high frequency sound regions than another passenger on the front seat (driver's seat or assistant driver's seat) because the former passenger will listen to sound in medium and high frequency sound regions derived only from the front loudspeakers.
Then, if the sound volume is adjusted with reference to the rear seat, then the sound volume on the front seat will be excessively great.
It is to be noted that, due to structural characteristics of a vehicle, if a loudspeaker of a great diameter is employed as a front loudspeaker, then it is mounted either in the dashboard or in a door of the vehicle, and in this instance, when the sound volume is great, resonance will occur and cause distortion of sound. Accordingly, a front loudspeaker is not suitable for reproduction of low frequency sound of a great sound volume.
On the other hand, a rear loudspeaker is suitable for reproduction of low frequency sound because the trunk room of the vehicle can be used as a loudspeaker box therefor.